To kick off my look at the best prospects in the minor leagues this week, I've ranked all 30 MLB farm systems from top to bottom, considering only the players who are currently in their systems and who have not yet exhausted their rookie of the year eligibility. (I use the same criterion for the individual player rankings that will be posted over the next three days.)

I've done these rankings for the past few years, and I was surprised at how few farm systems there were this year that had both impact and depth, fewer than in any of the previous years in which I've gone through this exercise. Some of that reflects all of the major promotions that took place in 2012, but we've also hit a slightly down period in the cycle of farm system quality.

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